public class Point3D extends Point {
    private int z;
    
    public Point3D() {
        this(0, 0, 0);
    }

    public Point3D(int x, int y, int z) {      // constructor
        super(x, y);
        this.z = z;
    }

    // Returns true if o refers to a Point3D object with the same x/y/z
    // coordinates as this Point3D;  otherwise returns false.
    public boolean equals(Object o) {
        if (o != null && getClass() == o.getClass()) {
            Point3D p = (Point3D) o;
            return super.equals(o) && z == p.z;
        } else {
            return false;
        }
    }

    public int getZ() { return z; }

    public void translate(int dx, int dy, int dz) {
        super.translate(dx, dy);
        z += dz;
    }

    public String toString() {        // for printing
        return "(" + getX() + ", " + getY() + ", " + z + ")";
    }
}